The angular disposition of a sound source from a position directly in front of a listener to a position to the side of a listener is accompanied by audible amplitude increases in frequencies greater than ˜300 Hz at the near side (outer ear contributions), reduced amplitudes at the far side (because of the head shadow), and relative phase differences and arrival times to each ear. Such cues are used by the brain to locate angular or azimuth sound source positions relative to the listener. Additional cues created by outer ear geometry allow vertical sounds to be located.
Stereophonic playback inherently creates such cues for two loudspeaker locations as the sound sources that are correspondingly processed by the listener's brain. These cues psychoacoustically define an essentially flat two-dimensional soundstage that spans the area between the speakers.
The present invention relates to a new method and apparatus for accurately interfacing three-dimensional spatial cues inherently embedded in audio sources with a listener's cognitive psychoacoustic responses when the sources are played back through two loudspeakers.